Motor vehicles having internal combustion engines are most often started by means of an electrically powered starter motor which obtains its powering current from a battery which conventionally comprises several electrolytic battery cells containing plates submerged into an electrolyte. The battery is connected to the starter motor by means of a switch in an ignition lock which is switched on at turning a key.
It is however relatively difficult to protect such a conventional system against theft since the switch in the ignition lock can be by-passed in a simple manner. There is thus a need for alternative ways of protecting motor vehicles against theft. A possibility therefor is arranging an anti-theft device directly in or at the battery as will be apparent from the discussion below.